1. Field of the Invention
The present invention relates to an ink-jet printer's spraying device, that is, its cartridge's head, and more particularly, to a spraying device and method for an ink-jet printer, in which pigment particles are separated within ink using ultrasonic waves, electrically charged through a mesh grid, and then ejected using a potential difference of an electric field density selectively formed.
2. Description of the Prior Art
The structure and operational principle of a general inkjet printer will be described below with reference to FIG. 1.
An ink-jet printer has a CPU 10 for receiving a signal from a host computer (not shown) through its printer interface, reading a system program in an EPROM 11 that stores initial values for operating the printer and the overall system, analyzing the stored values, and outputting control signals according to the content of the program; a ROM 12 for storing a control program and several fonts; a RAM 13 for temporarily storing data during system operation; an ASIC circuit 20, which comprises most of the CPU-controlling logic circuitry, for transmitting data from the CPU 10 to the various peripheral components; a head driver 30 for controlling the operation of an ink cartridge 31 according to the control signals of the CPU 10 transmitted from the ASIC circuit 20; a main motor driver 40 for driving a main motor 41 and for preventing the nozzle of the ink cartridge 31 from exposure to air; a carriage return motor driver 50 for controlling the operation of a carriage return motor 51; and a line feed motor driver 60 for controlling the operation of a line feed motor 61 which is a stepping motor for feeding/discharging paper.
In the operation of the above apparatus, a printing signal from the host computer is applied through the printer interface thereof, to drive each of the motors 41, 51 and 61 according to the control signal of the CPU 10 and thus perform printing. Here, the ink cartridge 31 forms dots by spraying fine ink drops through a plurality of openings in its nozzle.
The ink cartridge 31, shown in FIG. 2, comprises a case 1, which forms the external profile of the cartridge, for housing a sponge-filled interior 2 for retaining the ink. Also included in the ink cartridge 31 is a head 3, shown in detail in FIG. 3, which has a filter 32 for removing impurities in the ink; an ink stand pipe chamber 33 for containing the filtered ink; an ink via 34 for supplying ink transmitted through the ink stand pipe chamber 33 to an ink chamber (see FIG. 5) of a chip 35; and a nozzle plate 111 having a plurality of openings, for spraying ink in the ink chamber transmitted from the ink via 34 onto printing media (e.g., a sheet of paper).
As illustrated in FIG. 4, besides the ink via 34, the head 3 includes a plurality of ink channels 37 for supplying ink from the ink via to each opening of the nozzle plate 111; a plurality of nozzles 110 for spraying ink transmitted through the ink channels 37; and a plurality of electrical connections 38 for supplying power to the chip 35.
As illustrated in FIG. 5, the head 3 includes a resistor layer 103 formed on a silicon dioxide (SiO.sub.2) layer 102 on a silicon substrate 101 and heated by electrical energy; a pair of electrodes 104 and 104' formed on the resistor layer 103 and thus providing it with electrical energy; a protective layer 106 formed on the pair of electrodes 104 and 104' and on the resistor layer 103, for preventing a heating portion 105 from being etched/damaged by a chemical reaction to the ink an ink chamber 107 for generating bubbles by the heat from the heating portion 105; an ink barrier 109 acting as a wall defining the space for flowing the ink into the ink chamber 107; and a nozzle plate 111 having an opening 110 for spraying the ink pushed out by a volume variation, i.e., the bubbles, in the ink chamber 107.
Here, the nozzle plate 111 and the heating portion 105 oppose each other with a regular spacing. The pair of electrodes 104 and 104' are electrically connected to a terminal (not shown) which is in turn connected to the head controller (FIG. 1), so that the ink is sprayed from each nozzle opening.
The thus-structured conventional ink spraying device operates as follows. The head driver 30 transmits electrical energy to the pair of electrodes 104 and 104' positioned where the desired dots are to be printed, according to the printing control command received through the printer interface from the CPU 10. This power is transmitted for a predetermined time through the selected pair of electrodes 104 and 104' and heats the heating portion 105 by electrical resistance heating (measured in joules) as determined by P=I.sup.2 R. The heating portion 105 is heated to 500.degree. C.-550.degree. C., and the heat conducts to the protective layer 106 thereon. Here, when the heat is applied to the ink directly wetting the protective layer, the distribution of the bubbles generated by the resulting steam pressure is highest in the center of the heating portion 105 and symmetrically distributed (see FIG. 6). The ink is thereby heated and bubbles are formed, so that the volume of the ink on the heating portion 105 is changed by the generated bubbles. The ink pushed out by the volume variation is expelled through the opening 110 of the nozzle plate 111.
At this time, if the electrical energy supply to the electrodes 104 and 104' is cut off, the heating portion 105 is momentarily cooled and the expanded bubbles are accordingly contracted, thereby returning the ink to its original state.
The ink thus expanded and discharged out through the openings of the nozzle plate is sprayed into the printing media in the form of a drop, forming an image thereon due to surface tension. In doing so, internal pressure is decreased in accordance with the volume of the corresponding bubbles discharged, which causes the ink chamber to refill with ink from the container through the ink via.
However, the above-described conventional ink spraying device has several problems. First, since bubbles are formed in the ink by high-temperature heating and the ink itself exhibits a thermal variation, the lifetime of the head is decreased due to an impact wave from the bubbles. Second, the ink and the protective layer 106 react electrically with each other, resulting in corrosion due to migrating ions from the interface of the heating portion 105 and the electrodes 104 and 104', which thereby further decreases the lifetime of the head. Third, the influence of bubbles being formed in the ink chamber containing ink increases the ink chamber's recharging time. Fourth, the shape of the bubbles affects the advance, circularity and uniformity of the ink drop, which therefore affects printing quality.
Moreover, the ink spraying device as described above, being a thermal type, has certain inherent disadvantages. For example, the employed ink must be capable of operation at very high temperatures and without any resulting changes in its characteristic properties. Further, such ink requires a long drying time after each printing operation due to the volume of liquid (pigment carrier) in the ejected ink. Also, in the construction of the device, the basic configuration of the heating chambers and ink chambers, which make up an array of nozzles, necessitates a difficult alignment and bonding process between two elements of fabrication and consumes valuable wafer space which is limited.